Impact Of Postoperative Elective Nodal Irradiation In Pathologically Node Negative Early Stage Squamous Carcinoma Of The Oral Tongue

The risk of regional recurrence in early stage (pT1-2pN0) squamous cell carcinoma of the oral tongue (OTSCC) is high even after adequate neck surgery, especially in tumors with deep invasion (DOI). Whether postoperative elective nodal irradiation (ENI) in these patients can improve regional control is still unknown. This retrospective study sets to evaluate the role of ENI in regional control in pT1-2pN0 OTSCC. Cases of OTSCC referred to Queen Elizabeth Hospital between 2004 and 2015 were extracted from the Hong Kong Cancer Registry. Inclusion criteria were pT1-2 and pN0 (AJCC 7th Edition) and primary surgery with at least an ipsilateral selective neck dissection. ENI is defined as a radiation dose of ≥ 50 Gy (EQD2) to ipsilateral level I and II or more. Independent review of the DOI of each tumor was carried out by the pathologists from the referring hospitals according to the definition set out in the AJCC 8th Edition staging manual. Regional control and survival outcomes were evaluated using log-rank test and the cox proportional hazard model. A total of 511 patients diagnosed with OTSCC were identified within the study period. 55 of them fulfilled the inclusion criteria. Median follow up was 72.9 months. 16 (29.1%) patients received ENI while 39 (70.9%) did not. ENI was not correlated with tumor grade, perineural invasion, or lymphovascular invasion, but DOI was significantly deeper for patients who received ENI (median 6.5 mm vs 10.5 mm, Mann-Whitney U, p < 0.001). When stratified by a DOI cut-off of 5 mm, the 5-year regional control is not significantly different (81.8% for < 5mm vs. 87.4% for ≥ 5 mm, p = 0.65). 5-year regional control rate with ENI is numerically higher, though statistical significance is marginal (100% vs. 80.5%, p = 0.076). Despite having a statistically significant deeper DOI, patients who received ENI had comparable regional control to those without. ENI may negate the negative prognostic impact of deep DOI. Further prospective validation study is warranted.